Cognitive radio is a paradigm that has recently been introduced to improve the spectrum utilization for wireless communications by allowing a network or a wireless node to alter its transmission and/or reception parameters to utilize a licensed band when licensed activity is absent, thereby allowing cognitive radio users to communicate efficiently while avoiding interference with licensed or unlicensed users. Generally, the cognitive radio user successively monitors the dynamic usage of the licensed frequency band and utilizes it when the licensed activity is absent. When the cognitive radio user determines that licensed activity is absent, the cognitive radio user alters its transmission and/or reception parameters to use the licensed frequency band. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behavior, and network state.
A periodic sensing framework is usually adopted such that each frame of the cognitive radio user consists of a sensing block and an inter-sensing block. The inter-sensing block is used for data transmission after a licensed frequency band is identified as being unoccupied in the sensing block.
The cognitive radio user typically maintains constant transmit power levels in the inter-sensing block (for data transmission) and stops transmission as soon as the next sensing block is scheduled. Maintaining constant transmit power levels until the next sensing block is scheduled, however, may cause interference with the licensed user. For example, as the ending moment of the data block in the inter-sensing period approaches, the licensed user has a higher probability to reoccupy the frequency band. If the licensed user attempts to utilize the licensed frequency band prior to the end of the data transmission by the cognitive radio user, then the cognitive radio user's transmission may interfere with the licensed user.
Accordingly, there is a need for a power control system and method that takes into consideration the non-interfering probability, thereby improving the bandwidth efficiency and suppressing interference.